Keep in mind that it's my impression that, much like the G3258, the xx90 "Haswell refresh" CPUs (e.g. i5-4690/k, i7-4790/k, etc) may require an updated BIOS in order to boot on 80-series LGA1150 motherboards but will always "just work" on 90-series LGA1150 motherboards.
It's also worth mentioning that, if one is considering to spend more money for something better than a G3258, then it might make more sense to instead go for something newer like 2017's 2core/4thread budget PC gaming champion the Pentium G4560 or, if wanting to use integrated graphics, the Pentium G4600 or G4620 since the G4560 has a substantially weaker iGPU:
And to be clear, the G4560, G4600, and G4620 cannot be overclocked, but they have higher stock clocks than the G3258 and also perform a little better in terms of performance-per-GHz, and also go for similarly-cheap prices.
Really the price issue then would be the motherboard since you'd need a 100-series LGA1151 motherboard with an updated BIOS or 200-series motherboard instead which is very likely to be more expensive than an 80-series or 90-series LGA1150 motherboard, and the vast majority of 100-series LGA1151 motherboards used DDR4 which will additionally cost more than the dirt-cheap DDR3 that's available on the used market (though there were some rare 100-series LGA1151 motherboards that actually used DDR3...)
Speaking of which, the iGPU on Haswell Pentiums is substantially cut down compared to their i3/i5/i7 counterparts with something like half of the shader count:
In terms of non-overclockable CPUs, Xeon CPUs can be substantially cheaper than their equivalent i5/i7 - just keep in mind that not all Xeon CPUs come with integrated graphics; heck, it looks like you can even get various 3.4-3.5GHz 4core/8thread 4th gen Haswell Xeon CPUs for like $20 to $30 USD on ebay which is kind of nutty to be honest and, at least for multi-threaded performance, might be the real price-vs-performance deal for a non-overclocked CPU (keeping in mind that the 1220, 1225, and 1226 are "only" 4core/4thread rather than 4core/8thread, and that Dolphin would still be faster on even a measly Pentium G4600) - I wonder if it's because they're now over 8 years old and so tons of workstations that used 4th gen Haswell Xeon CPUs have and are being decommissioned?:
Skylake 6th gen Xeon CPUs are also cheap but, beginning with that generation, Intel were jerks with their product segmentation (what else is new...) and you could no longer use a desktop Xeon on a consumer motherboard, requiring the use of something like a C236 chipset motherboard (which admittedly can be had on ebay for relatively cheap but those boards have anemic VRM cooling, possibly under the assumption they'd be paired with low-powered CPUs for things like digital signage):
Thing is though, once you start getting to above $50 on a CPU, it starts making more sense to go with lower-end new stuff since the main benefit nowadays of higher end CPUs is having additional cores but, as we've well established, most of those additional cores aren't really useful for Dolphin and you'd need more GPU performance to tackle something higher-end (Ryzen APUs could probably be fine, but even the lower end Ryzen 2200G still goes for around $60 USD on ebay).
With all this CPU stuff being said, if entertaining the idea of higher-end LGA1150 DDR3 CPUs, then do not forget about 5th gen Broadwell which is notable specifically for their stronger integrated graphics (albeit still weaker than a Ryzen 2200G), remembering that the Xeon varients are not overclockable and even the i5 and i7 models do not overclock nearly as well as 4th gen Haswell; also 5th gen Broadwell definitely requires a BIOS update to boot on 80-series motherboards but similarly "just works" on 90-series motherboards:
Oh and uh, funny thing about it being easier to use the 1st party GameCube USB adapter on Linux - it seems that, with the flatpak version of Dolphin, you need to run Dolphin as root in order for it to see the adapter... (it just says "Access Denied (insufficient permissions)")
So you might want to stick with the PPA unless you know how to make the Dolphin flatpak always launch with root permissions.
It's also worth mentioning that, if one is considering to spend more money for something better than a G3258, then it might make more sense to instead go for something newer like 2017's 2core/4thread budget PC gaming champion the Pentium G4560 or, if wanting to use integrated graphics, the Pentium G4600 or G4620 since the G4560 has a substantially weaker iGPU:
And to be clear, the G4560, G4600, and G4620 cannot be overclocked, but they have higher stock clocks than the G3258 and also perform a little better in terms of performance-per-GHz, and also go for similarly-cheap prices.
Really the price issue then would be the motherboard since you'd need a 100-series LGA1151 motherboard with an updated BIOS or 200-series motherboard instead which is very likely to be more expensive than an 80-series or 90-series LGA1150 motherboard, and the vast majority of 100-series LGA1151 motherboards used DDR4 which will additionally cost more than the dirt-cheap DDR3 that's available on the used market (though there were some rare 100-series LGA1151 motherboards that actually used DDR3...)
Speaking of which, the iGPU on Haswell Pentiums is substantially cut down compared to their i3/i5/i7 counterparts with something like half of the shader count:
In terms of non-overclockable CPUs, Xeon CPUs can be substantially cheaper than their equivalent i5/i7 - just keep in mind that not all Xeon CPUs come with integrated graphics; heck, it looks like you can even get various 3.4-3.5GHz 4core/8thread 4th gen Haswell Xeon CPUs for like $20 to $30 USD on ebay which is kind of nutty to be honest and, at least for multi-threaded performance, might be the real price-vs-performance deal for a non-overclocked CPU (keeping in mind that the 1220, 1225, and 1226 are "only" 4core/4thread rather than 4core/8thread, and that Dolphin would still be faster on even a measly Pentium G4600) - I wonder if it's because they're now over 8 years old and so tons of workstations that used 4th gen Haswell Xeon CPUs have and are being decommissioned?:
- https://en.wikipedia.org/wiki/List_of_Intel_Xeon_processors_(Haswell-based)#%22Haswell-WS%22_(22_nm)
Skylake 6th gen Xeon CPUs are also cheap but, beginning with that generation, Intel were jerks with their product segmentation (what else is new...) and you could no longer use a desktop Xeon on a consumer motherboard, requiring the use of something like a C236 chipset motherboard (which admittedly can be had on ebay for relatively cheap but those boards have anemic VRM cooling, possibly under the assumption they'd be paired with low-powered CPUs for things like digital signage):
- https://www.anandtech.com/show/9730/intel-launches-greenlow-c236-chipset-and-skylake-e31200-v5-xeons
Thing is though, once you start getting to above $50 on a CPU, it starts making more sense to go with lower-end new stuff since the main benefit nowadays of higher end CPUs is having additional cores but, as we've well established, most of those additional cores aren't really useful for Dolphin and you'd need more GPU performance to tackle something higher-end (Ryzen APUs could probably be fine, but even the lower end Ryzen 2200G still goes for around $60 USD on ebay).
With all this CPU stuff being said, if entertaining the idea of higher-end LGA1150 DDR3 CPUs, then do not forget about 5th gen Broadwell which is notable specifically for their stronger integrated graphics (albeit still weaker than a Ryzen 2200G), remembering that the Xeon varients are not overclockable and even the i5 and i7 models do not overclock nearly as well as 4th gen Haswell; also 5th gen Broadwell definitely requires a BIOS update to boot on 80-series motherboards but similarly "just works" on 90-series motherboards:
- https://en.wikipedia.org/wiki/Broadwell_(microarchitecture#Desktop_processors
- https://en.wikipedia.org/wiki/List_of_Intel_Xeon_processors_(Broadwell-based)#%22Broadwell-H%22_(14_nm)
Oh and uh, funny thing about it being easier to use the 1st party GameCube USB adapter on Linux - it seems that, with the flatpak version of Dolphin, you need to run Dolphin as root in order for it to see the adapter... (it just says "Access Denied (insufficient permissions)")
So you might want to stick with the PPA unless you know how to make the Dolphin flatpak always launch with root permissions.
Dolphin 5.0 CPU benchmark
CPU: Pentium G3258 @ 4.5GHz 1.24v
GPU: Intel integrated
RAM: 4x4GB Corsair Vengence @ DDR3-1600
OS: Linux Mint of some variety + [VM] Win7 SP1 x64
CPU: Pentium G3258 @ 4.5GHz 1.24v
GPU: Intel integrated
RAM: 4x4GB Corsair Vengence @ DDR3-1600
OS: Linux Mint of some variety + [VM] Win7 SP1 x64